Adjustable stripper with stroke control

ABSTRACT

A punch press includes a fluid actuator operable to reciprocate a punch through advance and return strokes relative to a die to punch holes in an intervening workpiece. A stripper is supported by the press to prevent upward movement of the workpiece on the return stroke of the punch and is adjustable vertically relative to the die to accommodate different thicknesses of workpieces. A proximity detector carried by and adjustable with the stripper detects the return of the lower end of the punch upwardly past the stripper and in response to such detection, produces a signal controlling the actuator to terminate the return stroke of the punch.

United States Patent 1 Scott 1March 13, 1973 ADJUSTABLE STRIPPER WITH STROKE CONTROL [75] Inventor: William B. Scott, 650 Race Street,

Rockford, Ill.

[73] Assignee: W. A. Whitney Corp., Rockford, Ill.

[22] Filed: Aug. 2, 1971 [21] Appl. No.: 168,099

Primary Examiner-J. M. Meister AttorneyWolfe, Hubbard, Leydig, Volt & Osann, Ltd.

[57] ABSTRACT A punch press includes a fluid actuator operable to reciprocate a punch through advance and return strokes relative to a die to punch holes in an intervening workpiece. A stripper is supported by the press to prevent upward movement of the workpiece on the return stroke of the punch and is adjustable vertically relative to the die to accommodate different thicknesses of workpieces. A proximity detector carried by and adjustable with the stripper detects the return of the lower end of the punch upwardly past the stripper and in response to such detection, produces a signal controlling the actuator to terminate the return stroke of the punch.

3 Claims, 4 Drawing Figures PATENTEUHAR 1 31m SHEET 2 BF 2 INVENTOR. lV/{MI/I/Z fad/2' ADJUSTABLE STRIPPER WITH STROKE CONTROL BACKGROUND OF THE INVENTION This invention relates to a stripper which is used with a punch press to strip a workpiece from a punch carried on the end of a ram as the latter reciprocates through its return stroke after driving the punch through the workpiece and into an underlying die to punch a hole in the workpiece. More particularly, the invention relates to a stripper which is adjustable toward and away from the die so as to change the distance between the endof the stripper and thedie to accommodate workpieces of different thicknesses. In such a press, it is also desirable to adjust the length of the return stroke of the punch when the press is changed over to operate on a workpiece of a different thickness. That is, it is desirable to keep the return stroke of the punch as short as possible in order to reduce the time required to complete each punching cycle.

SUMMARY OF THE INVENTION The primary object of the present invention is to adjust the return stroke of the punch automatically as an incident to the adjustment of -.the stripper thereby to eliminate the need of the press operator having to make a separate stroke adjustment after adjusting the stripper.

Another object is to detect the return of the lower end of the punch to a predetermined positionabove the lower end of the stripper regardless of the spacing between the stripper and the die and, in response to such detection, to terminate the return stroke of the punch.

A further object is to provide a proximity detector which is carried by and adjustable with-the stripper for detecting when the punch reaches the predetermined distance and which, in response to such detection, produces a signal controlling further operations of the press.

These and other objects and advantages of the present invention willbecome more apparent from the following detailed description when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary side elevational view of a punch press embodying the novel features of the' DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in the drawings for purposes of illustration, the invention is incorporated in a punch press having a fluid-operated actuator 11 supported on a horizontal mounting plate 13 and operable to reciprocate a movable tool element 14 through advance and return strokes relative to an underlying fixed tool element 15 cooperating with the movable tool element to perform a machining operation on a workpiece 16 such as a piece of sheet metal disposed between the two elements. Herein, the fixed tool element is a female die mounted in a die holder 17 and supported within a flat bed 19 in a position vertically aligned with the movable tool element which is a punch adapted to telescope downwardly into the die and punch out holes in the workpiece when moved through the advance stroke by the actuator.

As shown most clearly in FIGS. 1 and d, the fluidoperated actuator 11 includes a cylinder 20 disposed above the mounting plate 13 and a piston 21 adapted for up and down reciprocation in the cylinder in response to the admission of pressure fluid into the cylinder alternately on opposite sides of the piston through conduits 23 and 24 communicating through a four-way control valve 25 (FIG. 4) with a suitable pressure source 26 for supplying pressurized oil to the cylinder. Anchored to the lower end of the piston and extending through the mounting plate is a piston rod or ram 27 whose lower end is connected to the punch 14. The upper end of a stripper housing 29 (see FIG. 2) is connected to the underside of the mounting plate 13, the ram being telescoped through the housing and the punch being movable through a stripper 30 carried on the lower end of the housing to limit upward movement of the workpiece 16 on the return stroke of the punch and thereby strip the workpiece from the punch.

The advance stroke of the ram 27 is initiated in response to a signal from a conventional numerical control system (not shown) as an incident to the workpiece 16 being moved into a proper position beneath the punch 14. Such signal energizes a solenoid 28 (FIG. 4) which shifts the valve 25 in a direction admitting pressure fluid from the source 26 through the upper conduit 23 and into the upper end of the cylinder 20 to force the piston 21 toward the lower end of the cylinder and thereby advance the ram. Once the ram reaches the end of its advance stroke, the solenoid 28 is deenergized, the valve is reversed and fluid is-directed through the lower conduit 24 to force the piston to move toward the upper end of the cylinder so as to retract the ram upwardly within the stripper housing 29 by a lower proximity detector 31 (FIG. 2) which detects the arrival of the ram to a preselected position located below the lower end of the cylinder such that the punch 14 is allowed to travel through the workpiece 16 and into the die 15 while the piston 21 is prevented from completely bottoming out in the lower end of the cylinder and causing damage to the cylinder.

Herein, the detector 31 is supported on the lower end of an elongated bracket 33 (FIG. 2) attached to a cylindrical shield 35 depending from the plate 13 so that the detector is held in a fixed vertical position relative to the lower end of the cylinder 20. The detector extends horizontally into the stripper housing 29 through a vertically elongated slot 34 formed in the side of the housing. The slot enables vertical adjustment of the stripper housing without-having to move the detector. In its fixed vertical position, the detector senses the presence of a lower reference member 36 upon the arrival of the ram 27 to its preselected position below the lower end of the cylinder. As shown in FIG. 2, the reference member is a metal lug held in a fixed position on the side of the ram. In response to the detection of the lug, the proximity detector 31 produces a Signal to de-energize the upper solenoid 28 and to energize a lower solenoid 39 which is operable when energized to shift the valve 25 to direct pressure from the pressure source 26 into the lower end of the cylinder 24 and thereby terminate the advance stroke and initiate the return stroke of the ram back up into the stripper housing 29.

As shown in FIG. 1, the stripper housing 29 is a cylindrical sleeve with a cut-away, open side 40 for ease in changing the punch 14 and includes a U-shaped lower end portion 41 carrying the stripper 30. Herein, the stripper resembles a heel-shaped plate which includes a center hole 43 (FIG. 2) sized to allow passage therethrough of the punch. The stripper is slidable horizontally out of the housing for removal and replacement with strippers having different sizes of center holes to accommodate punches of different diameters. A horizontal lip 44 extends outwardly from the stripper and fits into a complementary groove 45 formed in the inner wall of the lower end portion of the housing to hold the stripper vertically within the housing. A set screw 46 holds the stripper against horizontal movement. When held in the housing, the lower end surface 47 of the stripper extends downwardly beyond the bottom edge of the lower end portion and normally is spaced slightly above the top surface of the workpiece 16 (see FIG. 2) to allow the workpiece to he slid in above the die and to limit the upward movement of the workpiece as the punch is retracted upwardly through the stripper hold 43 on the return stroke of the ram 27.

To accommodate different thicknesses of workpieces, the stripper 30 is adjustable vertically with the housing 29 for movement toward and away from the die 15. This is accomplished by means of a spur gear 49 (FIG. 2) which includes outer gear teeth 50 connected by a horizontal web 51 to a central drum 53. The latter acts as a turnbuckle between the upper end of the stripper housing and a coupling sleeve 54 bolted to the underside of the mounting plate 13. Thus, when the gear is turned, the drum moves vertically relative to the sleeve and the housing is moved vertically relative to the drum to adjust the stripper with respect to the die. As shown more specifically in FIG. 2, the sleeve 54 and spur gear are enclosed and protected by the cylindrical shield 35 and the lower end portion of the sleeve is threaded with an external right-hand thread 55. The inner wall of the central drum 53 includes internal right and left-hand threads 56 and 57, the right-hand thread extending upwardly from the vertical center of the drum and the left-hand thread extending downwardly from the vertical center of the drum. Thus, the upper end portion of the drum is threaded over the lower end portion of the sleeve and is movable up and down on the sleeve simply by turning the spur gear.

The stripper housing 29 is carried with the drum 53 by means of a collar 59 (FIG. 2) which is bolted to a peripheral flange 60 on the upper end of the housing.

The collar includes an external left-hand thread 61 mated with the internal left-hand thread 57 of the drum to connect the housing for vertical movement with the gear 49. A locator rod 63 (FIG. 3) depending from the lower edge of the sleeve 54 fits slidably through an opening 64 extending through the collar to prevent angular movement of the stripper housing relative to the sleeve. Thus, as the gear 49 is turned to thread the drum 53 vertically on the sleeve 54, the collar 59 is threaded also in a corresponding direction within the lower end of the drum thereby doubling the vertical movement of the stripper housing 30 with respect to the die as compared to the vertical movement of the gear. In other words, when the spur gear is threaded vertically on the sleeve to move a predetermined distance, the stripper housing, being carried by the gear, is also moved vertically that same distance. At the same time, the collar is threaded within the drum and moves a corresponding equal distance relative to the drum and this distance is added to the first distance with the result that, for every unit of distance the gear moves vertically, the stripper moves two units of distance in the same direction.

To turn the spur gear 49, the outer teeth 50 of the gear mesh with the teeth of a drive gear 65 mounted on the upper end of the drive shaft 66 of a hydraulic motor 67. The latter is supported beneath the mounting plate 13 on the lower end of a bracket 69 whose upper end is fastened to the plate as shown in FIG. 2. When the motor is driven, the drive gear turns the spur gear and, as the spur gear moves vertically, the drive gear remains in a fixed vertical position with the teeth of the drive and spur gears splining together to allow the spur gear to move vertically relative to the drive gear. Thus, it will be seen that the distance between the stripper and the die may be adjusted to accommodate different thicknesses of workpieces by actuating the motor to drive the spur gear which then threads up or down on the sleeve and, at the same time, threads the collar 59 in or out of the drum 53 to move the stripper housing 29 carrying the stripper 30.

When changing over the press 10 to perform work on workpieces of different thicknesses, it is desirable also to change the length of the return stroke of the ram 27. In accordance with the present invention, the length of the return stroke of the ram is adjusted automatically as an incident to the vertical adjustment of the stripper 30. For this purpose, a proximity detector 70 is carried on and adjustable with the stripper housing 29 and produces a signal which terminates the return stroke of the ram 27. when the lower end of the punch 14 has been retracted upwardly out of the workpiece and just beyond the lower surface 47 of the stripper 30. Because the proximity detector is carried on the stripper housing, vertical adjustment of the stripper to conform to the thickness of the workpiece serves also to adjust the vertical position of the detector so that, regardless of the thickness of the workpiece, the return stroke of the punch will always be stopped just after the punch has been retracted out of the workpiece but before the punch travels an unnecessary distance above the workpiece. Accordingly, the upper limit of the return stroke is adjusted in accordance with the thickness of the workpiece to stop the punch just above the workpiece and thereby reduce the time required for each punching cycle-and yet such adjustment is achieved automatically as an incident to adjusting the stripper and without need of making a separate adjustment.

In the present instance, the proximity detector 70 (FIG. 3) is disposed above the detector 31 and produces a signal in response to detecting the presence of an upper reference member 71 which moves with the ram 27 as the latter is reciprocated through its advance and return strokes. In carrying out the invention, the upper detector 70 is supported by the stripper housing 29 a fixed distance upwardly from the stripper 30 so that, as the stripper is adjusted vertically, the upper detector is adjusted automatically to produce a signal when the upper reference member reaches a different position relative to the die 15. As shown in FIG. 3, the upper detector is mounted on the sidewall of the housing by a nut 73 and extends through the wall with the inner end of the detector protruding towards the ram. The upper detector is of conventional construction and serves to produce an electrical signal when the reference member reaches a predetermined position with respect to the detector.

The upper reference member 71 herein is a lug which is formed of metal and which triggers the upper detector 70 when raised by the ram 27 into a position substantially horizontal with the upper detector as shown in FIG. 3. The lug is fastened to the ram in a slot 74 by a set screw so that the outer radial end of the lug is spaced from the inner end of the upper detector to avoid wear between the lug and the upper detector. Moreover, the lug is located a distance upwardly from the lower end of the punch 14 approximately equal to or slightly less than the fixed distance that the upper detector is located above the stripper. Thus, when the lug is aligned horizontally with the upper detector, the lower end of the punch is located flush with or just upwardly of the lower surface 47 of the stripper.

Coincident with and in response to the detection of the lug 71, the detector 70 emits an electrical signal which de-energizes the solenoid 39 to center the valve 25 so as to stop the flow of pressure fluid into the lower end of the cylinder 20 and terminate the return stroke of the ram 27. Thus, the return stroke of the ram is limited vertically as the lug aligns horizontally with the upper detector and the lower end of the punch is retracted upwardly past the lower surface 47 of the stripper 30. In other words, the stroke of the ram is limited to the minimum length necessary for the thickness of the workpiece 16 being punched and this length is automatically adjusted with the vertical adjustment'of the stripper.

The signal produced by the detector 70 also initiates operation of the numerical control system to re-position the workpiece 16 for another punching cycle. Accordingly, by adjusting the position of the detector when the stripper 30 is adjusted for workpieces of different thickness, wasted time in initiating the workpiece re-positioning cycle is avoided since such cycle is started as soon as the punch 14 clears the workpiece.

While the present invention has been described in conjunction with a proximity detector 70 as being mounted on the stripper housing 29, it will be appreciated that other sensing mechanisms will work equally well in controlling the length of the return stroke of the ram 27. For instance a mechanical limit switch controlling the actuation of the valve 25 could 10 justing the height of the stripper 30 to accommodate workpieces of different thicknesses. Thus, the cycle time of a punching operation is reduced to a minimum without requiring the punch press operator to make a separate adjustment to control the return stroke of the ram with each corresponding adjustment of the stripper.

I claim as my invention:

1. In a press having a ram reciprocable downwardly and upwardly in a cylinder in response to pressure fluid being admitted into and dumped from the upper end of the cylinder, said ram carrying a tool which coacts with an underlying die to perform a piercing operation on an intervening workpiece on the downstroke of the ram, a stripper located above the workpiece for stripping the latter from the tool on the upstroke of the ram, said stripper being mounted for vertical adjustment relative to the die to enable positioning of the lower end of the stripper at different elevations to accommodate workpieces of different thicknesses, the improvement in said press comprising, means carried by and adjustable with said stripper for detecting the return of the lower end of the tool a predetermined distance upwardly from the lower end of the stripper regardless of the elevation of the stripper, and said means being operable in response to such detection to produce a signal controlling the flow of pressure fluid to said cylinder to terminate the upstroke of the ram.

2. In a press having a ram reciprocable through advance and return strokes with one end of said ram carrying a tool which coacts with an adjacent die to perform a piercing operation on an intervening workpiece on the advance stroke of the ram, a stripper having one end located adjacent the tool for stripping the workpiece from the tool on the return stroke of the ram, said stripper being mounted for adjustment toward and away from the die to enable positioning of the one end of the stripper at different distances from the die'to accommodate workpieces of different thicknesses, the improvement in said press comprising, and sensing means carried by and adjustable with said stripper and operable to produce an electrical signal in response to detecting the return of the tool a predetermined distance past the one end of the stripper regardless of the distance between the one end of the stripper and the die.

3. A press as defined by claim 2 including a reference member attached to and carried with said ram, said means including a proximity detector movable with said stripper and operable to detect the presence of said reference member when said ram moves through the return stroke and to produce said signal in response to such detection. 

1. In a press having a ram reciprocable downwardly and upwardly in a cylinder in response to pressure fluid being admitted into and dumped from the upper end of the cylinder, said ram carrying a tool which coacts with an underlying die to perform a piercing operation on an intervening workpiece on the downstroke of the ram, a stripper located above the workpiece for stripping the latter from the tool on the upstroke of the ram, said stripper being mounted for vertical adjustment relative to the die to enable positioning of the lower end of the stripper at different elevations to accommodate workpieces of different thicknesses, the improvement in said press comprising, means carried by and adjustable with said stripper for detecting the return of the lower end of the tool a predetermined distance upwardly from the lower end of the stripper regardless of the elevation of the stripper, and said means being operable in response to such detection to produce a signal controlling the flow of pressure fluid to said cylinder to terminate the upstroke of the ram.
 1. In a press having a ram reciprocable downwardly and upwardly in a cylinder in response to pressure fluid being admitted into and dumped from the upper end of the cylinder, said ram carrying a tool which coacts with an underlying die to perform a piercing operation on an intervening workpiece on the downstroke of the ram, a stripper located above the workpiece for stripping the latter from the tool on the upstroke of the ram, said stripper being mounted for vertical adjustment relative to the die to enable positioning of the lower end of the stripper at different elevations to accommodate workpieces of different thicknesses, the improvement in said press comprising, means carried by and adjustable with said stripper for detecting the return of the lower end of the tool a predetermined distance upwardly from the lower end of the stripper regardless of the elevation of the stripper, and said means being operable in response to such detection to produce a signal controlling the flow of pressure fluid to said cylinder to terminate the upstroke of the ram.
 2. In a press having a ram reciprocable through advance and return strokes with one end of said ram carrying a tool which coacts with an adjacent die to perform a piercing operation on an intervening workpiece on the advance stroke of the ram, a stripper having one end located adjacent the tool for stripping the workpiece from the tool on the return stroke of the ram, said stripper being mounted for adjustment toward and away from the die to enable positioning of the one end of the stripper at different distances from the die to accommodate workpieces of different thicknesses, the improvement in said press comprising, and sensing means carried by and adjustable with said stripper and operable to produce an electrical signal in response to detecting the return of the tool a predetermined distance past the one end of the stripper regardless of the distance between the one end of the stripper and the die. 